Multilevel presses, which comprise a multiplicity of horizontal press platens disposed between fluid-operated cylinder-and-piston arrangements and a head plate or bed plate, are common in the production of pressed board, the layers of material to be pressed being deposited upon these platens, e.g. on a press underlay of sheet or tray form, so that closure of the press results in compaction to form the pressed product on the underlay.
The platens of the press may be heated to activate a binder which can be incorporated in the material to be pressed or applied between layers to be bonded together.
Simultaneous-closure arrangements can be provided on the press to ensure uniform reduction of the distances between the successive platens during press closure.
Presses and installations of this type are disclosed inter alia in commonly assigned applications Ser. No. 127,572 filed Mar. 6, 1980, now U.S. Pat. No. 4,289,467, Ser. No. 185,181 filed Sept. 8, 1980 and Ser. No. 207,429 filed Nov. 17, 1980, as well as in the U.S. Pat. Nos. 3,565,725, 3,409,942, 3,396,783, 3,332,819, 3,428,505, 3,241,189, 3,050,777, 3,224,758, 3,077,271, 3,050,200, and 3,860,381. Other art dealing with this subject matter can be found in the United States Patent Office Manual of Classification classes and subclasses to which these patents and applications are assigned and in the files thereof.
For the purposes of this disclosure, reference to a multilevel press will mean a press as described above, whether or not equipped with control, simultaneous-closure, heating and cooling and other systems as described in the aforementioned publications and applications. Reference to the production of pressed board in such presses will include the production of particle board and fiber board, with or without added thermally activatable binders, using wood chips, sawdust, cellulosic fibers or other materials commonly utilized in the mats of pressable materials.
It will also include the production of pressed board of any density and thickness, ranging from high strength structural particle board of high density, to low-strength, low-density board suitable primarily for use as insulation.
It will also include production of laminates in which, for example, a decorative or protective foil, e.g. of synthetic resin material may be laminated to a substrate by heat and pressure, the substrate being particle board, for example, or the production of more complex laminates in which, for instance, metal foils, patterning foils or the like are employed with or without embossing of the surface of the laminate.
Reference to press underlays is intended to include the generally thin, relatively flat members in sheet or tray form used heretofore and includes textile underlays, sheet metal underlays, metal screen underlays and like textured or patterned underlays. The sole criteria for an underlay in the sense of the present disclosure is that a layer of pressable material can be deposited thereon and carried by the underlay into the press, the underlay remaining in the press during the pressing operation and the pressed body being thereafter removed e.g. upon the underlay which can be reused.
Multilevel presses or multiplaten presses of the aforedescribed type have been associated with multilevel discharge racks or frames which are disposed adjacent the press. The pressed products from each level or platen, upon opening of the press is transferred from the press onto a corresponding level of the multilevel emptying or discharge rack.
The discharge rack thus can have its platforms or spaced positioned to correspond, i.e. to be level with, the platens of the press in the open condition thereof while individual board-transfer devices can be associated with each press level to effect the transfer.
It is also known in such systems to store the press underlays after removal of the pressed products and to feed the press underlays back onto the respective press platens.
Interruptions in the operation of the press frequently requires opening of the press to prevent damage to (e.g. burning of) the pressed products.
In earlier systems, the storage device for the press underlays was an independent unit brought into the region of the press when required to accept the underlays upon such interruptions. Such systems are of course expensive and require large amounts of space. They also complicate the control systems for introducing the press underlays into the storage unit.
Mention can be made of rotating underlay storage devices for screen-type underlays which store the screen in a lower pass. All of these arrangements are relatively complicated and prone to breakdown. This applied as well to storage units such as suspended screen magazines. In operation, these devices tend to retard productivity of the plant.